Managing Risk: VFR Versus VMC

Are you prepared for when the weather deteriorates?

By Michael Vivion

It has been a long day on a long cross-country flight. The weather forecasts have not been very accurate—you’re reminded of a quote from an anonymous wag: "Weather forecasts are horoscopes with numbers." Low ceilings and fog delayed your departure, and now you’ll be pushing sunset to reach your destination. Nevertheless, the weather has remained basic VFR, although lowering ceilings have forced you to fly at a lower altitude than you flight-planned. As the flight progressed, you’ve gotten more comfortable with this low altitude.

As you approach the last ridgeline nearing your destination, the visibility starts to diminish in mist. You notice tendrils of fog forming ahead and below you. Forty minutes ago, the METAR at your destination indicated basic VFR conditions. Barely. You recall that the temperature and dew-point spread at that time was one degree. You’re 15 miles from your destination as the sun approaches the horizon. The better visibility the METAR reported must be just around this next ridge. But as you clear the ridge a few miles from your destination, you find yourself suddenly in instrument meteorological conditions at low level, in terrain. Historically, that has been a recipe for disaster. The pilot described in this vignette had no intention of flying into poor weather, but weather flying can be one of the most challenging aspects of VFR flight.

Improving Training A significant part of pilot training involves interpretation of weather data and weather-related decision making. General aviation accidents involving poor pilot weather decision-making account for about four percent of the total accidents each year, but as reported by the AOPA Air Safety Foundation, they represent 14% of the fatal mishaps. Unfortunately, basic flight training doesn’t always provide the pilot all the tools needed to operate safely in VFR weather.

I’ve lost track of the number of pilots with whom I’ve discussed marginal weather flying during flight reviews who firmly asserted that they’ll never fly in marginal weather. While this may represent their best intentions, sometimes events overcome us, and it’s important to be prepared.

There are a couple of areas where I think we could do better in both initial and recurrent pilot training. Pilots need to develop a better understanding of weather terminology as well as weather theory. Too many instructors simply teach the material that’s tested on the FAA Knowledge Test.

It’s Legal, But Is It Safe? In the regulations, visual flight rules are a set of operating rules that require reported ceilings to be at least 1,000 feet and visibility to be three miles or more for operation under VFR. These criteria change, depending on the class of airspace in which we’re operating, but the salient point here is that the regulations simply provide minimum criteria, which must be met to operate legally. Just because the weather meets these criteria doesn’t suggest that it’s safe to fly under VFR.

What VFR pilots really care about is whether we can remain clear of clouds and see ahead well enough to maintain a wings-level attitude and navigate by visual references. That’ll depend on ceiling and visibility, of course, but also to some degree, it’ll depend on the kind of terrain over which we’re operating. A better term for these conditions is VMC, or visual meteorological conditions. We obviously care about the regulatory criteria, but what’s equally important is whether we can see well enough to operate safely. When someone uses the term “VFR weather,” what comes to your mind? I would bet that most pilots don’t visualize three miles’ visibility and overcast at 1,100 feet. Yet those are the conditions in which we can legally operate throughout much of the U.S. airspace.

Unfortunately, most pilots are never exposed to true marginal weather during their flight training. Flight in three or four miles’ visibility can be very disorienting, and the perspective from 500 or 600 feet AGL presents a very different view and a different set of challenges than flight at 5,000 feet AGL.

Consider the conditions encountered flying on the East Coast in the heat of summer, or Southern California, when visibilities often are less than three or four miles. Whether they know it or not, most pilots are relying much more heavily on their instruments than they may realize. Even though conditions may be above basic VFR, the failure of a GPS, a vacuum failure or electrical failure could easily precipitate a very real emergency, or at least some uncomfortable moments. The development of powerful GPS systems has made pilots perhaps braver than they might be if they were navigating by pilotage. All we have to do is follow that little pink line, right? But GPS units do fail.

Managing Weather What can the prudent pilot do to improve his or her weather savvy? First, pilots need to better understand the definitions used in weather forecasts. For example, in a forecast, what does the term “occasional” really mean, as opposed to "frequent" or "intermittent?" An understanding of the definitions and basic forecast terminology is essential to successfully understanding the available weather products. Know how to accurately read and interpret forecasts, because you’re going to fly in the weather they describe.

Take advantage of the many excellent weather tools available via the Internet. The National Weather Service offers powerful weather-evaluation tools on its website Aviation Digital Data Service, at http://aviationweather.gov/adds. There are many other free and pay-as-you-go weather tools out there. Find one you like and use it regularly. Learn everything you can about meteorology and forecasting, so that you can become a better evaluator of forecasts and a better forecaster in your own right.

When planning for a flight, determine what the current conditions are, and what they’re most likely to become, over the route of flight and the time frame covered by the flight. What are the weather trends? What’s the next significant weather feature headed that way? When is that next system expected to arrive over the route?

Next, determine whether those conditions are adequate to safely transit the proposed route of flight. Basic VFR conditions in the prairie states may result in IMC in mountains. When the flight takes us over water or trackless terrain, even five miles’ visibility may not be adequate for safe operation. What are the alternates and the options if the weather deteriorates while you’re en route?

To develop your weather-evaluating skills, check weather forecasts for your local area even on days when you don’t intend to fly. Then watch the weather as the day progresses. Was the forecast accurate? If not, how was it inaccurate: in what the weather did, or in when it changed? When you’re driving or looking out the window, imagine what that view would be like in an aircraft operating under VFR. The idea is to learn to picture what forecasted weather actually looks like.

On days when you opt not to fly because of forecast inclement weather, pay attention to the actual weather conditions as the day progresses. Again, rate the forecast accuracy and your decision making. This’ll not only help you to visualize weather conditions based on a forecast, but also help you to improve your own forecast-evaluation skills.

Find a competent instrument instructor who’s willing to do some VFR flying on a marginal day. Use good judgment in your choice of places to fly and the weather in which you fly. Study the country on a clear day in advance, so that you have a good hazard map of obstacles and their heights prior to flying on a poor-weather day. Above all, be sure that you have the option of safely transitioning to IFR or landing if need be. This experiment will further assist you in visualizing weather from the cockpit. The idea of this exercise isn’t to train you to fly in marginal conditions, but rather to show you just how ugly marginal VFR conditions can be, and how disorienting and dangerous those conditions can be. The idea is to encourage you to avoid those conditions.

Having and maintaining options is essential when operating in lowering weather conditions. Knowing where that nearest airport is, what the heading back to better weather is and what the terrain is like around you is essential situational awareness. Don’t allow yourself to get into lowering conditions without good situational awareness, and lots of options.

Finally, it’s advisable to get an instrument rating and stay as current on instruments as your budget will permit. An instrument rating is no guarantee of immunity, however—every year, a few instrument-rated pilots succumb to what the NTSB refers to as “continued VFR flight into IMC” and fly their aircraft into a mountain or other object, albeit right side up.

If you find yourself entering marginal VFR, perform a strategic retreat, and the earlier, the better. The transition to marginal conditions often comes close to the destination, when the pilot is reluctant to give up. This is precisely when never allowing yourself to fly into conditions without a “plan B” and being willing to exercise it pays off.

Good weather-evaluation skills should help avoid marginal conditions; and good training, some structured exposure to marginal weather conditions and a good set of alternates can save the day if you do get into lowering conditions.

Mike Vivion served as a wildlife biologist/pilot in Alaska for nearly 30 years. He now coordinates the aviation program and flight-instructs at the University of Minnesota in Crookston. He’s a caretaker of a modified 1952 Cessna 170.